[moTthediesel]

I've been wondering for some time -- how much should you rely on the EGT to select gears when driving for max mpg?

Of course I know that for the most part, the highest gear you can drive in smoothly will yield the best efficiency, but when watching the pyrometer while climbing hills - I sometimes wonder.

For instance, say I'm climbing a fairly steep hill at 55 mph - I can stay in top gear (4th in my case) and the engine will not be lugging, but it may be showing 900 F on the gauge. I could shift down to 3rd, maintain the same speed, and the EGT would drop to 600 F.

So is the EGT reading a reliable measure of how much fuel is being burned? Or - does the reading go down in 3rd just because the engine is breathing more and cooling the combustion chamber, even though more fuel is being burned?